Method of purifying electrolytes



Patented Mar. 12, 1946.

2,396,509 METHOD OF PURIFYIN G ELECTROLYTES Dinsmor'e Laurence Griflith and Luther Glenn Hendrickson, Flin Flon; signers to Hudson Bay Company Limited, Winnipeg, Manitoba, Can- Manitoba, Canada, as-

Mining and smelting ada, a corporation of Canada No Drawing. Application August 9, 1943, Serial N0. 497,980

2 (ll aims.

The present invention relates to a method of purifyingelectrolytes. More particularly, 'it relates to a method of purifying zinc electrolytes and especially to electrolytes as used in the electrolytic method of winning zinc from ores or other materials.

That certain impurities in electrolytes cause reat difliculty during the operation of plating by electrical methods, in some cases due to the im-.

purity itself plating and so causing the deposit to be impure and of less value, and in other cases due to the impurity bringing about a lowered efilciency in the plating process, is a fact well known in the arts. Consequently, great pains are taken and much expense is incurred in purifying electrolytes so that the harmful impurities may be removed to a sufilcient extent.

In the electrolytic process for the winning of zinc, for example, the impurities cadmium, copper, tin, arsenic, antimony, lead, and other elements, if left in the electrolyte, will deposit along with the zinc in the electrolytic cell and will render the zinc impure so that its value is decreased; other impurities, among which may be mentioned arsenic, antimony, tin, germanium, tellurium, se lenium, iron, nickel, and cobalt, lower-the efiiciency of the electrolysis so that more current is used to produce a pound of metalthan would, be required'if'theseelements were abSent and so theirpresence greatly increases the expense of the process. Commonly, two and sometimes three' processes are used to remove these impurities.

The iron, together with part of the copper, arsenic,

antimony, tin, germanium, tellurium, selenium, and other metals, is precipitated by treating the electrolyte with zinc oxide, or roasted zinc ore, or lime, while air is blown through the solution.

or filters. The solution is then treated with 'zinc as copper salts, and antimony, arsenic, tellurium, selenium, tin, cobalt, copper, cadmium, and other elements-are precipitated and may be removed by filtration. Sometimes a third method is used to remove certain elements, as, for example, sometimes a nitroso-B-naphthol 4s used to remove cobalt.

Now,- in the i'emoval of impurities by means of zinc dust, it is well known in the art that the purifying action of zinc dust is increased if finely divided copper be present; commonly this finely The resulting precipitate is removed by thickeners divided copper is formed by precipitating it from the solution to be purified by thezinc dust. Further, the purifying action of the zinc is still fur' ther increased if antimony or arsenic be deposited precipitates in such aiform that the cake 5 minutes. .The issuing upon it: when zinc dust, together with copper and antimony, is used, the purifying action becomes great-enough to precipitate certain metals, of

which cobalt is an example, which are very dimcult to precipitate otherwise.

We have discovered that tin may be used in: stead of antimony or arsenic, and that tin has certain advantages which make it to be preferred to either arsenic or antimony. In the first place,

10 tindoes not tend to dissolve'in-the purification,

process to as great an extent as does arsenic or antimony and if it does dissolve, it is more easily removed by further treatment. Secondly, tin does not bring about as great a lowering of current efficiency in' the electro-deposition of zinc as does'antimony; in this respect it is more similar to arsenic. Thus, if some of :the metal doesset into solution during the purification process, then tin is lessdangerous than antimony. Thirdly, tin of zinc dust-copper-tin plus impurities is more easily filtered than the corrdsponding cakes produced when antimony or arsenic is used: this feature is extremely important if .the purification is carried out. by drawing the solution to be purified through a. layer or cake of the purifying agent.

As an example'of the use of our invention, we

took a sample of zinc electrolytewhich showed the following analysis as to impurities:

so Milligrams per liter Cobalt 7.9 Arsenic 0.12 Antimony 0.03 Tin Trace and 8 grams of copper sulphate in water and then added 200 grams of zinc dust'which passed a 20.- mesh screen and was caught in a 48-mesh screen.

dust, sometimes along withother reagents such The mixture was agitated until the copper was precipitated, then the supernatant liquid was decanted on. The zinc dust, coated with copper and tin, was thenpacked into a l-inch copper ;tube about 12 inches long and held in place with glass wool. Arrangements were made so that the electrolyte could be drawn through this copper tube. The electrolyte was hinted to 50 C. and drawn through; the contact with the mixture is estimated to have been 0.44 solution had the following I We dissolved 0.277 gratnof staunous chloride time of the electrolyte That the tin plays as essential role in the purification was proved by carrying'out the same experiment, using zinc dust alone, copper only, and the alone; the issuing solution had the analysis:

or zinc dust and same electrolyte. With zinc Milligrams per liter Cobalt 7.9 Arsenic 0.06 Antimony 0.03 10 With zinc dust coated with copper, the issuing solution had the analysis:

It will be observed that in the precipitants above described, including zinc coated with copper; the precipitant atlnely divided form held in a porous bed, which has the eii'ect of holding the precipitated impurities in contact with the purifying agent, by which means a degreeoi improved purification is obtained.

What we'claim is:

1. In the purification of zinc electrolytes by means or metallic precipitants: the step of contacting the electrolyte with zinc dust coated with copper and tin as the precipitant.

2. A method of purifying zinc electrolytes by means of metallic precipitants comprising passing the electrolyte through a stationary'porous mass of finely divided precipitant for the electrolyte comprising zinc dust coated with copper and tin, and maintaining the precipitated impurities in contact with the precipitants while continuing to pass the electrolyte through said mass.

DINSMORE LAURENCE GRIFFITH. LUI'HER GLENN HENDRICKSON. 

